Spatially selective uhf near field microstrip coupler device and rfid systems using device

ABSTRACT

A system having a UHF RFID transceiver is adapted to communicate exclusively with a single electro-magnetically coupled transponder located in a predetermined confined transponder operating region. The system includes a near field coupling device comprising a plurality of lines connected in parallel with an unmatched load. The near field coupling device may be formed, for example on a printed circuit board with a plurality of electrically interconnected traces and a ground plane. The system establishes, at predetermined transceiver power levels, a mutual electro-magnetic coupling which is selective exclusively for a single transponder located in a defined transponder operating region. Also included are methods for selective communication with the transponder in an apparatus such as a printer-encoder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/133,801, filed Jun. 5, 2008, which is a divisional of U.S.application Ser. No. 10/604,996, filed Aug. 29, 2003, which is herebyincorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to RFID systems, operable with a variety ofdifferent dimensioned electro-magnetically coupled transponders, workingat close proximity, to an RF transceiver antenna that is spatiallyselective for an individual transponder located in a predeterminedtransponder operating region to the exclusion of other adjacenttransponders, and its application to printers-encoders or other systemsutilizing such in UHF RFID systems.

2. Description of Related Art

UHF radio frequency identification (RFID) technology allows wirelessdata acquisition and or transmission from and or to active (batterypowered) or passive transponders using a backscatter technique. Tocommunicate with, i.e., “read” from and or “write” commands and/or datato a transponder, the transponder is exposed to an RF electro-magneticfield by the transceiver that couples with and energizes (if passive)the transponder through electro-magnetic induction and transferscommands and data using a predefined “air interface” RF signalingprotocol.

When multiple passive transponders are within the range of the same RFtransceiver electro-magnetic field they will each be energized andattempt to communicate with the transceiver, potentially causing errorsin “reading” and or “writing” to a specific transponder in the readerfield. Anti-collision management techniques exist to allow nearsimultaneous reading and writing to numerous closely groupedtransponders in a common RF electro-magnetic field. However,anti-collision management increases system complexity, cost and delayresponse. Furthermore, anti-collision management is “blind” in that itcannot recognize where a specific transponder being processed isphysically located in the RF electro-magnetic field, for example, whichtransponder is located proximate the print head of a printer-encoder.

One way to prevent errors during reading and writing to transponderswithout using anti-collision management is to electrically isolate aspecific transponder of interest from nearby transponders. Previously,isolation of transponders has used RF-shielded housings and/or anechoicchambers through which the transponders are individually passed forpersonalized exposure to the interrogating RF field. This requires thatthe individual transponders have cumbersome shielding or a significantspatial separation.

RFID printers-encoders have been developed which are capable ofon-demand printing on labels, tickets, tags, cards or other media withwhich a transponder is attached or embedded. These printer-encoders havea transceiver for on-demand communicating with the transponder on theindividual media to read and/or store data into the attachedtransponder. For the reasons given, it is highly desirable in manyapplications to present the media on rolls or other format in which thetransponders are closely spaced. However, close spacing of thetransponders exacerbates the task of serially communicating with eachindividual transponder without concurrently communicating withneighboring transponders on the media. This selective communicationexclusively with an individual transponder is further exacerbated inprinters-encoders designed to print on the media in or near the samespace as the transponder is positioned when being interrogated.

When transponders are supplied attached to a carrier substrate, forexample in RFID-attached labels, tickets, tags or other media suppliedin bulk rolls, Z-folded stacks or other format, an extra length of thecarrier substrate is required to allow one transponder on the carriersubstrate to exit the isolated field area before the next transponder inline enters it. The extra carrier substrate increases materials costsand the required volume of the transponder media bulk supply for a givennumber of transponders. Having increased spacing between transpondersmay also slow overall printer-encoder throughput.

When transponders of different sizes and form factors are processed, theRF shielding and or anechoic chamber configuration will also requirereconfiguration, adding cost, complexity and reducing overallproductivity. In certain printer-encoders it is desired to print ontransponder-mounting media in the same transponder operating region inwhich the transponder is being read from or written to. This may be verydifficult to accomplish if the transponder also must be isolated in ashielded housing or chamber.

UHF transponders may operate in, for example, the 902-928 MHz band inthe United States and other ISM bands designated in different parts ofthe world. For example, in FIG. 1 a conventional one-half wavelength“Forward Wave” microstrip prior art coupler 3 consisting of a, forexample, rectangular conductive strip 5 upon a printed circuit board 7having a separate ground plane 9 layer configured for these frequencies.One end of the conductive strip 5 is connected to transceiver 42 and theother end is connected through terminating resistor 8 to ground plane 9.The conductive strip 5 as shown in FIG. 1 has a significant width due toRF design requirements imposed by the need to create acceptablefrequency response characteristics. This type of prior art coupler 3 hasbeen used with UHF transponders that are relatively large compared tothe extent of prior art coupler 3.

As shown by FIGS. 2 a and 2 b, recently developed transponders 1,designed for operation at UHF frequencies, have one dimension sosignificantly reduced, here for example a few millimeters wide, thatthey will be activated upon passage proximate the larger prior artcoupler 3 by electro-magnetic power leakage 10 concentrated at eitherside edge of the conductive strip 5 of prior art coupler 3. In FIG. 2A,the two leakage regions “A” and “B” defined by electro-magnetic powerleakage 10 are small and relatively far apart, increasing system logicaloverhead and media conveyance positioning accuracy requirements. If thetransponders 1 were placed close together, then multiple transponders 1might be activated by the physically extensive one-half wavelength“Forward Wave” microstrip prior art coupler 3.

Thus the minimum required spacing of these transponders 1 to isolatethem, and thus the minimum size of media 11 (assuming that they areembedded one per label or media 11 on carrier substrate 13) must belarge relative to the size of the microstrip coupler 3. This createsissues for media suppliers by limiting the available space on the media11 for transponder 1 placement and significantly increasing thenecessary accuracy of the transponder 1 placement within and or underthe printable media 11 and along the liner or carrier substrate 13. Thisalso reduces the cost advantages of using the narrow dimensionedtransponder(s) 1 within media 11, as the media 11 must be much largerthan the transponder 1 to achieve adequate RF isolation.

Competition in the market for such “integrated” printer-encoder systemsas well as other RFID interrogation systems has focused attention on theability to interrogate with high spatial selectivity any transponderfrom a wide range of available transponders having different sizes,shapes and coupling characteristics as well as minimization of overallsystem, media size, and transponder costs.

Therefore, it is an object of the invention to provide a device,systems, and methods that overcome deficiencies in such prior art.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a top view of a prior art microstrip forward wave coupler.

FIG. 2 a is a simplified cut-away side view of a transponder-couplerstructure using a prior art forward wave coupler as shown in FIG. 1,illustrating schematically locations where coupling with a narrowdimensioned transponder supplied in-line with other transponders on acarrier substrate may occur.

FIG. 2 b is a partial cut-away top schematic view of the prior artforward wave coupler and carrier substrate with embedded transponders ofFIG. 2 a.

FIG. 3 is a side schematic view of a media printer according to oneembodiment of the invention having an improved RFID interrogationsystem.

FIG. 4 a is a top view of a coupler according to one embodiment of theinvention.

FIG. 4 b is a top view of a coupler according to another embodiment ofthe invention.

FIG. 5 a is a simplified cut-away side view of a transponder-couplerstructure using a coupler according to the invention, illustratingschematically the spaced apart areas where coupling with a narrowdimensioned transponder supplied in-line with other transponders on acarrier substrate may occur.

FIG. 5 b is a partial cut-away top schematic view of the coupleraccording to the invention and carrier substrate with embeddedtransponders of FIG. 5 a.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns apparatus and method which enables anRFID transceiver (sometimes termed herein an “interrogator”) tocommunicate selectively and exclusively with a single UHF transponder 1when one or more other similar transponders are in close proximity,without the need for physical isolation or cumbersome shielded housingsor chambers.

The invention is useful in the reading and or data loading of UHFtransponders, for example on an assembly line, in distribution centersor warehouses where on-demand RFID labeling is required, and in avariety of other applications. In many applications a transponder or anumber of transponders are mounted or embedded on or in a label, ticket,tag, card or other media carried on a liner or carrier. It is oftendesirable to be able to print on the media before, after, or duringcommunication with a transponder. Although this invention is disclosedhere in a specific embodiment for use with a direct thermal or thermaltransfer printer, it may also be used with any type of spatiallyselective RFID interrogation device or other types of printers usingother printing technologies, including inkjet, dot-matrix, andelectro-photographic methods.

In some applications a print station may be at a distance from the RFIDtransceiver; in others it may be necessary to accomplish the printfunction in the same target space occupied by the transponder when it isbeing interrogated.

FIG. 3 illustrates by way of example only an implementation of theinvention in a thermal transfer media printer 16 in which both printingand transponder communication are accomplished, but at differentlocations in the media printer 16. The media printer 16 includes aprinthead sub-assembly comprising a conventional thermal printhead 18and platen roller 19, as in a direct thermal printer for printing onthermally-sensitive media. A web 24 of media 11, such as labels,tickets, tags or cards, is directed along a feed path 26 under theprinthead 18 where on-demand printing of text, bar codes and/or graphicstakes place under control of a computer or microprocessor (not shown).After being printed, the media 11 follows a media exit path 34 and maybe peeled off the underlying carrier substrate 13 at a peeler bar 32.The liner or carrier substrate 13 for the media is guided out of themedia printer 16 by a roller 36 where it exits the printer along acarrier exit path 38.

When a thermal printer is configured for use as a thermal transferprinter, a ribbon supply roll 28 delivers a thermal transfer ribbon (notshown for clarity) between printhead 14 and the media on web 24. Afteruse, the spent ribbon is collected on a take-up reel 22.

In accordance with an aspect of the present invention, the media printer16 includes a transceiver 42 for generating RF communication signalsthat are fed to a frequency and spatially selective microstrip nearfield coupler 30 located proximate the media feed path 26. As will beexplained and illustrated in detail hereinafter, the system (includingtransceiver 42 and near field coupler 30) forms a near field pattern inthe location of a transponder operating region C (see FIG. 5A). Thesystem is configured to establish at predetermined transceiver powerlevels a mutual coupling which exclusively activates and communicateswith a single transponder 1 located in the transponder operating regionC.

As labels or other media 11 with embedded transponders 1 move along themedia feed path 26 through transponder operating region “C”, data may beread from and or written to each transponder 1. Information indicia thenmay be printed upon an external surface of the media 11 as the mediapasses between the platen roller 19 and the printhead 18 by selectiveexcitation of the heating elements in the printhead 18, as is well knownin the art. When the media printer 16 is configured as a direct thermalprinter, the heating elements form image dots by thermochromic colorchange in the heat sensitive media; when the media printer 16 isconfigured as a thermal transfer printer, then ink dots are formed bymelting ink from the thermal transfer ribbon (not shown for clarity)delivered between printhead 18 and the media on web 24 from ribbonsupply roll 28. Patterns of printed dots thus form the desiredinformation indicia on the media 11, such as text, bar codes orgraphics.

Media conveyance is well known in the art. Therefore the mediaconveyance 25 portion of the printer that drives the media withtransponders along the media feed path 26 is not described in detail.

The near field coupler 30 according to the invention and its manner ofoperation will now be described with reference to FIGS. 4 a-5 b. Oneembodiment of the near field coupler 30 is configured for use, forexample, with UHF RFID transponders. The RFID transponders 1 may be bulksupplied on a carrier substrate 13 attached to or embedded within label,ticket, card or tag media 11.

The near field coupler 30 comprises an array of lines 50, as shown inFIGS. 4 a and 4 b. The near field coupler 30 is configured as a segmentof unmatched line 50 upon a dielectric substrate, for example a printedcircuit board 7, having a ground plane 9 formed on a spaced apartisolated layer, for example the reverse side of the printed circuitboard 7. One end of the array of lines 50 is connected to thetransceiver 42; the other end is connected to the ground plane 9 bymeans of terminating resistor 8.

Rather than operating as a standing wave radiating antenna, or magneticfield generating coil, the near field coupler 30 according to theinvention operates as a one half wavelength unmatched transmission linewith, for example, a 15 ohm characteristic impedance that is terminatedby a R=50 ohm terminating resistor 8. Signals generated by thetransceiver 42 passing along the transmission line generate a near fieldeffect emanating from the transmission line edges that couples with atransponder 1 passing through the transponder operating region. Anotherdescription for the near field effect is “leaky”, as discussed in “LeakyFields on Microstrip” L. O. McMillian et al. Progress inElectromagnetics Research, PIER 17, 323-337, 1997 and herebyincorporated by reference in the entirety. Because the near field effectis extremely local to the transmission line and degrades at anexponential rate with increasing distance from the transmission line,the resulting transponder operating region of a single transmission lineis very narrow. According to the invention, the prior rectangularconductive strip is therefore replaced with an array formed by aplurality of commonly fed and terminated, i.e. electrically parallel,line(s) 50, as shown for example in FIGS. 4 a and 4 b. The plurality ofline(s) 50 therefore creates an array of leaky edges as shown in FIG. 5a; each leaky edge creating an electro-magnetic power leakage 10 atseveral points within transponder operating region C. The resulting linearray has similar overall width to the prior solid microstrip coupler 3and may be similarly tuned, by adjusting the length, spacing anddielectric properties between the line(s) 50 and the ground plane 9 aswell as the number of line(s) 50 and or individual line widths, shapesand inter-spacing, to adjust the overall array as an integrated singleelectrical structure to have the desired frequency responsecharacteristics and generate a combined near field effect correspondingto a desired transponder operating region.

As shown by FIGS. 5 a and 5 b, the transponder operating region Cresulting from a near field coupler 30 according to the invention issubstantially uniform. Depending upon spacing between the lines andapplies power levels, narrow null gaps in the operational region C mayoccur, as illustrated by d, e, f, and g in FIG. 5 a. Simplified logicadded to the media transport system may be used to move the media 11forward a small increment, for example 1-2 millimeters if a transponder1 in the transponder operating region C falls upon one of these nullgaps and transponder communications is lost. These narrow null gaps areevidence of the extremely local field concentrations produced by thenear field effect and the precision with which the transponder operatingregion may be configured to have a wide area with sharply definedboundaries. These characteristics make the near field coupler 30 usefulfor eliminating precision transponder placement requirements for mediasuppliers, complex transponder location and tracking logic in mediasupply systems, as well as any requirements for shielding or increasedtransponder placement tolerance requirements. Further, the increasedtransponder operating region C provided by the present invention allowsusers increased freedom to place embedded transponder(s) 1 in media 11at desired locations, for example to avoid the printing degradation thatmay occur when the printhead encounters a media surface irregularity dueto the presence of a RFID transponder 1.

The array of lines 50 of the near field coupler 30 may be formed by aplurality of straight line(s) 50 as shown in FIG. 4 a. To further tunethe near field produced by the line(s) 50, a zig-zag or wiggle may beapplied to each line 50, as shown for example in FIG. 4 b to reduce theappearance and/or depth of the field strength gaps d, e, f and g. Forthe purpose of this specification, “zig-zag” is defined as acharacteristic of a line having an overall length characteristic, but aplurality of direction changes internal to the overall length of theline. The direction changes may, for example, be sharply defined oroccur as smooth curves.

Alternatively, a simplified transponder 1 read and or write system maybe formed without printing capabilities by positioning a near fieldcoupler 30 coupled to a transceiver 42 proximate a media conveyance 25moving sequential transponders 1 through a transponder operating regionC. This structure is also useful where the media 11 is unprinted, orprinted upon at another location.

The near field coupler 30 is not limited to a dual plane structure. Forexample, the near field coupler 30 may be co-planar, i.e. the groundplane and the array of lines 50 may be located, electrically isolatedfrom each other, in the same plane of a printed circuit board but ondifferent traces. Also, the lines 50 need not be co-planar, but may forma 3-dimensional structure. For example, the lines 50 may be on multiplelayers of a printed circuit board or formed as a wire frame of lines 50without use of printed circuit board technology.

Obviously, at some exaggerated transceiver power level, certaintransponders 1 outside the transponder operating region C may beexcited. However, by this invention, at appropriate power levels in therange of normal transponder read and write power levels the mutualcoupling created will be highly selective for the transponder 1 in thetransponder operating region C. By mapping and then applying only therequired power levels for a range of both different transponder 1 typesand positions within the transponder operating region C, energyconsumption and potential RF interference generation may be minimized.

The spatially-selective near field property and the lack of any othershielding requirements of the near field coupler 30 according to theinvention allows the economical addition of a compact,spatially-selective transponder communication module in devices such asprinter-encoders.

Because the near field coupler 30 may be configured to be selectiveexclusively for a single transponder located in the transponderoperating region C, it is now possible by this invention to use a web 24of media having transponders which are closely spaced on the web 24, asshown for example in the figures of this specification. Prior to thisinvention it was extremely difficult to communicate with just oneelectro-magnetically-coupled UHF transponder, which may have a widenumber of different physical configurations, in a closely spaced seriesof transponders without simultaneously activating adjacent transponders.

Where in the foregoing description reference has been made to ratios,integers or components having known equivalents then such equivalentsare herein incorporated as if individually set forth.

While the present invention has been illustrated by the description ofthe embodiments thereof, and while the embodiments have been describedin considerable detail, it is not the intention of the applicant torestrict or in any way limit the scope of the appended claims to suchdetail.

Additional advantages and modifications will readily appear to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative apparatus, methods,and illustrative examples shown and described. Accordingly, departuresmay be made from such details without departure from the spirit or scopeof the applicant's general inventive concept. Further, it is to beappreciated that improvements and/or modifications may be made theretowithout departing from the scope or spirit of the present invention asdefined by the following claims.

1. A printer including a transceiver adapted to communicate withtransponders, comprising: a printhead; a media conveyance adapted totransport a series of discrete media to said printhead and through atransponder operating region, at least some of said media including atransponder; a near field coupler configured to generate a near fieldeffect to couple with the transponder for data transfer; the near fieldcoupler having a plurality of lines electrically interconnected inparallel, and a spaced away ground plane.
 2. The printer defined byclaim 1 wherein the near field coupler is formed as traces on a printedcircuit board.
 3. The printer defined by claim 1 wherein the near fieldcoupler has a characteristic impedance and the near field coupler isterminated by a terminating resistor having a different characteristicimpedance.
 4. The printer defined by claim 1 wherein the plurality oflines are arranged parallel to each other.
 5. The printer defined byclaim 1 wherein at least one of the plurality of lines has a zig-zagconfiguration.
 6. The printer defined by claim 1 wherein said printheadis positioned and configured to print on or adjacent said transponderwhile it is still in said transponder operating region.
 7. The printerdefined by claim 1 wherein said printhead is positioned and configuredto print on or adjacent said transponder when it is outside of saidtransponder operating region.
 8. The printer defined by claim 1 adaptedto feed a web of spaced transponders through said transponder operatingregion, and wherein said printer communicates with a transponder locatedin said transponder operating region but concurrently not with anothertransponder located outside of said transponder operating region.